<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>

<div id="app">
    <p v-once>原始值：{{msg}}</p>
    <p>现在：{{msg}}</p>
    <input type="text" v-model="msg">

    <p>===================================</p>
    <p v-if="show">要</p>
    <p v-if="!show">不要</p>
</div>


<script src="js/vue.js"></script>
<script>
    new Vue({
        el: '#app',
        data: {
            msg: '今天天气很好!',
            show:true,
        }
    })
</script>
</body>
</html>